Continuously Producing Digital Micro-Scale Patterns On A Thin Polymer Film

ABSTRACT

A liquid thin film is disposed on a conveyor surface (e.g., a roller or belt) that moves the thin film into a precisely controlled gap (or nip) region in which the liquid thin film is subjected to an electric field that causes the liquid to undergo Electrohydrodynamic (EHD) patterning deformation, whereby portions of the liquid thin film form patterned liquid features having a micro-scale patterned shape. A curing mechanism (e.g., a UV laser) is used to solidify (e.g., in the case of polymer thin films, cross-link) the patterned liquid inside or immediately after exiting the gap region. The patterned structures are either connected by an intervening web as part of a polymer sheet, or separated into discreet micro-scale structures. Nanostructures (e.g., nanotubes or nanowires) disposed in the polymer become vertically oriented during the EHD patterning process. Segmented electrodes and patterned charges are utilized to provide digital patterning control.

FIELD OF THE INVENTION

This invention relates to micro-scale patterned structures, and moreparticularly to methods for producing micro-scale patterned structures.

BACKGROUND OF THE INVENTION

There is a growing need for methods of producing thin polymer films withthree-dimensional patterning at scales ranging from several microns tocentimeters in industrially relevant quantities. Such patterned polymerthin films are useful, e.g., for optical applications (anti-reflectivecoatings and filters) and controlled wetting applications (hydrophobicand hydrophilic applications).

There are a number of technologies that currently produce patterned thinfilms with topologies ranging from several hundred nanometers tomicrons, including rolling mask lithography (developed by Rolith, Inc.of Pleasanton, Calif., USA), Nanoimprint Lithography (Molecular Imprintsof Austin, Tex., USA and Obducat of Lund, Sweden), HolographicLithography (TelAztec LLC of Burlington, Mass., USA), and LiquidDeposition (“Sharkskin coater” at Fraunhofer Institute in Munich,Germany). All of these methods use master-based methods to create astructure in a photoresist film that is subsequently used to eitherdynamically create structure in glass, or in thin polymer films that canbe embossed and cured using UV light. None of these techniques are ableto create arbitrarily varying patterns in a large area format or in adynamic and digital manner.

Electrohydrodynamic (EHD) patterning is a recently developed technologythat involves electrically transferring the micro- or nano-structuresformed on a template onto a thin polymer film by shaping the surface ofthe liquid polymer film through a balance of applied forces on theliquid and the surface tension of the liquid. A surface instability canbe driven by van der Waals and thermal forces, but is typicallydominated by external forces, if those are present. All external (e.g.,electrical or thermal) forces that cause a pressure gradient across theinterface can cause this surface instability. The present inventionfocuses on EHD patterning techniques applied to polymer thin filmshaving a height/thickness that is much less than the length-scale of theinstability, so the kinetics of the polymer thin film are completelydescribed by lubrication theory, and the emerging pattern is driven bythe fastest growing capillary wave mode. The time scale for generatingsuch polymer thin film EHD patterning is dependent on the liquidpolymer's dielectric constant, viscosity, height/thickness and surfacetension, the applied voltage (electric field), and the distance betweenthe electrodes or charges used to generate the electric field, and thelength scale of the emerging pattern is dependent on the surfacetension, and the applied voltage and electric field inside the polymerfilm. These patterns can either occur at a length scale that isintrinsic to the film properties if the electric field is constant or beforced into specific structures if the electric field is spatiallyvaried. The height of replication for EHD patterning has been limited atthe nano-scale in previously proposed techniques because the electricfield is sensitive to the spacer height of the template. In addition,conventional EHD patterning techniques are not commercially viablebecause they are unable to produce commercially useful quantities offilm.

SUMMARY OF THE INVENTION

The present invention is directed to methods that implement improvedElectrohydrodynamic (EHD) thin film patterning techniques and provideviable and economical manufacturing techniques to continuously producingmicro-scale patterned structures that either integrally connected to athin polymer film or are separated from each other. The methods utilizetwo curved conveyors (e.g., two rollers or two belts) having opposingsurfaces that are spaced apart by a relatively large distances onopposite sides of a gap (or nip) region. A liquid thin film containing apolymer, a polymer precursor, or another suitable material, is coated orotherwise disposed onto one conveyor surface (e.g., the “lower” rolleror belt) by a suitable coating mechanism such that it is subsequentlyconveyed into the gap region, where the minimum gap distance between thetwo conveyor surfaces is set such a small gap is provided between theupper film surface and the opposing conveyor surface. As it passesthrough the gap region, the liquid thin film is subjected to an electricfield generated between the two conveyors, with the electric fieldstrength and liquid thin film characteristics (e.g., viscosity anddielectric constant) being set such that the liquid thin film undergoesEHD patterning (i.e., portions of the liquid polymer are pulled towardthe upper conveyor, thereby forming patterned micro-scale liquid polymerfeatures that extend from the lower conveyor into the small gap that isfilled with air or another fluid). An appropriate curing mechanism(e.g., a UV laser or thermal treatment) is utilized to cross-link (cure)the polymer thin film while undergoing EHD patterning (e.g., inside thegap region or immediately outside the gap region), whereby the liquidmicro-scale polymer features are hardened (solidified) to formmicro-scale patterned structures having the substantially the samepattern shape that was generated in the liquid polymer by the electricfield. The solid micro-scale patterned structures and any adjoiningpolymer thin film material are then removed from the lower conveyor. Thepresent invention thus provides a low-cost and efficient method forcontinuously producing digital micro-scale polymer structures that canbe utilized in a wide variety of commercial applications.

In accordance with a specific embodiment, the thin polymer film containsnanostructures (e.g., nanowires or nanotubes) that become verticallyoriented within the micro-scale structures. Specifically, thenanostructures have initial (e.g., random) orientations during thin filmformation, but become aligned within the micro-scale patterned structurein a substantially perpendicular orientation relative to the underlyingconveyor surface in response to the applied electric field and resultinghydrodynamic forces associated with EHD patterning formation ofmicro-scale features. This attribute makes the present invention highlyvaluable for the large scale production of certain devices that containspecialized nanostructures (e.g., carbon nanotubes for the production offlexible electronics interconnects or sensor arrays.

According to an alternative embodiment of the present invention,discreet (separate) micro-scale patterned structures are produced thatcan be used for example, in creating micron sized particles forincreased specificity in the delivery of drugs. The process involvesforming a polymer thin film so that the thin film is entirely formedinto features and breaks up into discreet liquid polymer “islands” asthe applied electric field causes vertical growth of the micro-scalefeatures (i.e., if insufficient liquid polymer surrounds thepillar-shaped micro-scale features, then the features become separatedfrom each other). Subsequent curing “freezes” (solidifies) the discreetfeatures to form a plurality of said solid micro-scale patternedstructures disposed in a spaced-apart arrangement on the lower conveyorsurface. The micro-scale patterned structures are then removed from theconveyor surface using a separating mechanism so that they can beincorporated into a target material.

In a practical embodiment, the upper and lower conveyors are implementedby parallel upper and lower cylindrical rollers, which are positioned bya nip (gap) system to define a precise nip distance. A UV cured polymerthin film is applied using a slot coater onto the lower roller, andcuring is performed by way of UV laser light after micro-scale featuresare established by EHD patterning in the nip region. This roll-to-rollproduction method allows for high production output using existing slotcoating systems and precision rollers, which minimizes manufacturingcosts.

According to another practical embodiment, the two conveyors areimplemented by belts positioned to define an elongated gap regionbetween opposing horizontally disposed belt sections. Thermosetting orUV curable polymer are applied upstream of the gap region, and curing isperformed by way of heating blocks or UV light transmitted throughtransparent belt material. In a specific embodiment, precise beltpositioning is achieved using a tongue-and-groove type arrangement inwhich T-shaped ribs extend below each belt and are slidably received incorresponding grooves formed in a belt support structure. Thisbelt-to-belt production method allows for longer pattern set-up periodsand higher production output rates than the roll-to-roll approach.

According to another embodiment, in order to achieve the mostflexibility in creating and controlling patterns, the present inventionutilizes a dynamic charge generation device that facilitate digitalcontrol over the patterning process. In accordance with one specificembodiment, the dynamic charge generation device includes an array ofsegmented electrodes disposed on the continuous-surface moving electrodestructure (e.g., an upper roller or belt), where each electrode isindividually addressable (i.e., each segmented electrode is individuallyaccessed by associated addressing lines). In other embodiments, chargepatterns are either directly deposited or created through aphoto-electric process on an insulated or dielectric surface of themoving electrode structure (e.g., by way of a scorotron), which providesthe benefits of reducing the sensitivity of the EHD pattern on theelectrode distance, enabling spatial modulation of the thin filmpatterns, and enabling temporal variations of the thin film patterns forcontinuous EHD patterning approaches. These digital patterning schemesallow the creation of coatings with arbitrary interactions with variouswavelengths of EM radiation across an object, or surfaces with spatiallyvarying wettability properties that act as passive pumps.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings, where:

FIG. 1 is a cross-sectional side perspective view depicting a method forgenerating micro-scale patterned structures according to a simplifiedembodiment of the present invention;

FIG. 2 is an enlarged cross-sectional side view showing a polymer thinfilm containing nanostructures;

FIG. 3 is an enlarged cross-sectional side view showing the formation ofmicro-scale patterned features containing the nanostructures of FIG. 2according to a specific embodiment of the present invention;

FIGS. 4(A), 4(B), 4(C), 4(D) and 4(E) are enlarged cross-sectional sideviews showing the formation of discreet micro-scale patterned featuresaccording to another specific embodiment of the present invention;

FIG. 5 is a perspective side view depicting roll-to-roll-type method forproducing micro-scale patterned structures according to a practicalembodiment of the present invention;

FIG. 6 is a cross-sectional side view depicting a belt-to-belt-typemethod for producing micro-scale patterned structures according toanother practical embodiment of the present invention;

FIG. 7 is a cross-sectional side view showing a portion of the systemshown in FIG. 6;

FIG. 8 is a cross-sectional side view showing a simplified method forproducing micro-scale patterned structures using separated electrodesaccording to another embodiment of the present invention;

FIG. 9 is a simplified perspective view showing a portion of thearrangement of FIG. 8; and

FIG. 10 is a cross-sectional side view showing a simplified method forproducing micro-scale patterned structures using applied charge patternselectrodes according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention relates to an improvement in methods for producingmicro-scale patterned structures for a variety of commercial purposes.The following description is presented to enable one of ordinary skillin the art to make and use the invention as provided in the context of aparticular application and its requirements. As used herein, directionalterms such as “upper”, “lower”, “upstream” and “downstream”, areintended to provide relative positions for purposes of description, andare not intended to designate an absolute frame of reference. Inaddition, the phrase “integrally connected” is used herein to describethe connective relationship between two portions of a single structure,and are distinguished from the terms “connected” or “coupled” (withoutthe modifier “integrally”), which indicates two separate structures thatare joined by way of, for example, adhesive, fastener, clip, or movablejoint. Various modifications to the preferred embodiment will beapparent to those with skill in the art, and the general principlesdefined herein may be applied to other embodiments. Therefore, thepresent invention is not intended to be limited to the particularembodiments shown and described, but is to be accorded the widest scopeconsistent with the principles and novel features herein disclosed.

The invention is described below with reference to exemplary methodsconfigured to produce EHD patterning conditions. Those skilled in theart will recognize that the parameters mentioned below are associatedwith specific experimental observations, and therefore are not intendedto be limiting.

FIG. 1 depicts an exemplary system 100 for illustrating a method ofcontinuously producing digital micro-scale patterned (polymer) featureson a thin film according to an embodiment of the present invention.System 100 generally includes a lower (first) conveyor 110, an upper(second) conveyor 120, associated conveyor drive mechanisms 130-1 and130-2, a thin film formation device 140, an electric field generator(indicated by low voltage source 150-1 and high voltage source 150-2),and an optional curing mechanism 160.

Conveyors 110 and 120 are implemented by any conveying devices (e.g.,such as rollers or belts) that provide a curved surface capable oftranslating (moving) a liquid polymer thin film through a narrow gapregion. Specifically, lower conveyor 110 has a lower (first) conveyorsurface 111 that is supported and constrained to move along acorresponding first curved (e.g., circular or oblong) path, and secondconveyor 120 has an upper (second) conveyor surface 121 that issupported and constrained to move along a corresponding second curvedpath. The curved paths associated with conveyors 110 and 120 arearranged such that conveyor surfaces 111 and 121 are separated byminimum distance G at a gap region 101, are separated by a relativelylarge first distance D1 at a “upstream” location from gap region 101,and a relatively large second distance D2 at an “downstream” locationfrom gap region 101, where distances D1 and D2 are much larger thanminimum gap distance G. For purposes that are described below, bothlower conveyor 110 and upper conveyor 120 comprise an electricallyconductive or dielectric material that maintains a potential across gapregion 101 during operation. In one embodiment, lower conveyor 110includes an electrically conductive metal or polymer, or is optionallycoated with an electrically conductive and transparent material such asIndium-Tin Oxide (ITO). Upper roller 120 also includes an electrodepattern (described below), or includes an electrically conductive metalor polymer.

According to an aspect of the invention, lower conveyor 110 and upperconveyor 120 are respectively driven by lower drive member 130-1 andupper drive member 130-2 (e.g., motors and/or belts) such that surfaces111 and 121 move at matching speeds through gap region 101.Specifically, surfaces 111 and 121 are moved along their respectivepaths such that each (first) surface region 111-1 of lower surface 111passes through gap region 101 substantially simultaneously with acorresponding (second) surface region 121-1 of upper surface 121.

Referring to the left side of FIG. 1, thin film formation device 140 isa coating device or other mechanism suitable for disposing a curableliquid polymer thin film 141L on lower conveyor surface 111 at a pointthat is upstream from gap region 101, whereby thin film 141L issubsequently conveyed into gap region 101 by normal movement of lowerconveyor 110. For example, device 140 deposits a thin film (first)portion 141-1 of a liquid polymer (e.g., polystyrene, polyvinyl alcohol(PVA), Polyvinylpyrrolidone (PVP), Polyethylene glycol (PEG) orOrmoStamp® UV cure polymer) on surface region 111-1 of lower conveyorsurface 111, and subsequent movement of lower conveyor surface 111causes portion 141-1 to move into gap region 101. In one embodiment,thin film formation device 140 is implemented by a slot coater thatreliably creates thin film 141L having a thickness (height) T (measuredfrom conveyor surface 111 to an upper surface 142 of thin film 141) inthe range of 1 to 100 microns). In other embodiments, other coatingdevices (e.g., a slot die coating system, a slide coating system, or acurtain coating system) that reliable create thin films having a fewmicrons thickness are used.

According to another aspect of the present invention, low voltage source150-1 and high voltage source 150-2 generate an electric field F betweenlower conveyor 110 and upper conveyor 120, for example, by respectivelyapplying a low voltage V1 and high voltage V2 (e.g., 0V and 100V,respectively) to the electrically conductive material disposed onconveyors 110 and 120. The strength of electric field F is determined bythe relative distance between the relatively low and relatively highcharges generated by voltages V1 and V2, which are indicated by “+” and“−” in FIG. 1 for descriptive purposes only (e.g., one of the chargesmay be 0V or the polarity of the charges may be reversed). That is, dueto the curved path followed by conveyor surfaces 111 and 121, electricfield F is highest (strongest) in gap region 101 (i.e., due to minimalgap distance G), and decreases (weakens) on either side of gap region101 in accordance with the associated spacing distance between surfaces111 and 121. In accordance with an aspect of the present invention,voltages V1 and V2 are selected such that electric field F is sufficientto cause polymer liquid thin film 141L to undergo EHD patterning(deformation) as polymer liquid thin film 141 passes into and throughgap region 101, thereby forming patterned liquid polymer features 143 inliquid polymer thin film 141L. Specifically, due to EHD patterning,patterned liquid polymer features 143 in the form of raised ridges orpillars are formed by liquid polymer drawn from surrounding portions ofthin film portion 141, whereby each patterned liquid polymer feature 143extends upward from conveyor surface 111 into gap region 101 (i.e.,toward upper conveyor 120). By controlling the strength of the electricfield F and by utilizing suitable polymer characteristics (e.g.,viscosity), patterned liquid polymer features 143 exhibit a micro-scalepatterned shape (i.e., the width and height of each patterned liquidpolymer feature 143 is on the order of 1 to 100 microns) in gap region101.

According to another aspect of the present invention, the EHD patternedliquid polymer features 143 and any surrounding polymer material arecured before the thin film polymer material passes out of electric fieldF. Referring to the right side of FIG. 1, curing mechanism 160 acts tosolidify each patterned liquid polymer feature 143 (i.e., when it islocated inside gap region 101, or immediately after it exits gap region101 but is still subjected to electric field F) and the surroundingpolymer material, thereby forming solid micro-scale patterned structures145 extending from solidified polymer thin film 141S, where eachmicro-scale patterned structure 145 has substantially the samemicro-scale patterned shape as that of its precursor liquid polymerfeature 143. The specific curing mechanism 160 utilized in each instanceis determined by the type of polymer material forming thin film 141L(e.g., if a UV curable polymer is used, then curing mechanism 160 isimplemented by a UV curing system, e.g., that directs a UV laser beam161 onto portions of thin film 141L disposed in gap region 101). Inother embodiments, depending on the type of polymer used, curingmechanism 160 is implemented by, for example, a visible light curingsystem or a focused thermal curing system.

Referring to the lower right portion of FIG. 1, subsequent to the curingprocess (i.e., downstream from gap region 101), solidified polymer thinfilm 141S is removed from lower conveyor 110 for further processing.Note that micro-scale patterned structures 145 remain spaced apart andextend upward from solidified polymer thin film 141S.

FIGS. 2 and 3 illustrate an unique attribute of the modified EHDpatterning method of the present invention in which “loaded” polymerthin films contain nanostructures that are inherently aligned during theformation of micro-scale polymer structures, thereby facilitating theproduction of a wide variety of highly valuable commercial applications.

FIG. 2 is a partial cross-sectional view showing a liquid polymer thinfilm portion 141L-1A including nanostructures 148 (e.g., carbonnanotubes or GaAs nanowires). In this case, a polymer/nanostructure thinfilm formation device 140A (e.g., one of coating systems mentioned abovethat is optimized to deposit the modified polymer/nanostructurematerial) forms liquid polymer thin film portion 141L-1A havingthickness T on lower conveyor 110 utilizing the methods similar to thosedescribed above with reference to FIG. 1. Note that nanostructures 148are dispersed with initial (e.g., random or non-random) orientationswithin liquid polymer thin film portion 141L-1A at deposition.

FIG. 3 shows liquid polymer thin film portion 141L-1A when it isdisposed in gap region 101 between lower conveyor 110 and upper conveyor120 in a manner similar to that described above with reference toFIG. 1. As described above, electric field F generated by voltagesources 150A-1 and 150A-2 causes EHD patterning deformation, wherebyliquid polymer material flows inward and upward (as indicated by thedashed-line arrows) to form a patterned liquid polymer feature 143 thatextends from liquid polymer thin film portion 141L-1A toward upperconveyor 120. In addition, when nanostructures 148 are reactive to anelectric field (e.g., carbon nanotubes), nanostructures 148 align inelectrical field F and couple to the hydrodynamic forces that resultfrom the pattern formation, producing a generally vertical orientation(i.e., generally perpendicular to surface 111 of lower conveyor 110).

To this point the present invention has been described with reference tothe fabrication of polymer thin films in which spacing between themicro-scale patterned structures is fixed by a thin polymer material towhich the micro-scale patterned structures are integrally connected, forexample, as shown in FIG. 1. Although such integral polymer thin filmsare believed to have many commercial applications such as thosementioned above, individual (separated) micro-scale patterned structuresare useful in other commercial applications (e.g., medicine).

FIGS. 4(A) to 4(E) are simplified cross-sectional views illustratingsystem 100B according to an alternative embodiment of the presentinvention that produces separated (discreet) micro-scale structures forthe creation of particles with increased specificity in the delivery ofdrugs.

FIG. 4(A) depicts a polymer thin film portion 141B1(t0) at an initialtime period (t0) on surface 111B of lower conveyor 110B. As in theprevious embodiments, polymer thin film portion 141B1(t0) is formed by aslot coater or other thin film formation device 140B (not shown) whilesurface 111B is separated from surface 121B of upper conveyor 120B byrelatively large distance D1. In the present embodiment, to cause thepolymer thin film to break up into discreet islands as described below,the polymer material forming polymer thin film portion 141B1(t0) has arelatively low viscosity and/or a thickness T1 of polymer thin filmportion 141B1(t0) is intentionally lower than that used in theembodiments described above.

FIG. 4(B) illustrates polymer thin film portion 141B1(t1) at a timeperiod (t1) subsequent to time t0 after being moved by lower conveyor110B into a position immediately upstream from the gap region, wheresurface 111B is separated from surface 121B by a relatively smalldistance D11. At this point the applied electric field F(t1) generatedby supplies 150B-1 and 150B-2 begins to cause EHD patterning of polymerthin film portion 141B1(t1), whereby the inward and upward flow ofliquid polymer generates a liquid micro-scale patterned feature143B(t1). Note that at time t1, due to its small size, sufficient liquidpolymer material surrounds patterned feature 143B(t1) to maintain acontinuous (although very thin) web-like portion 141B11.

FIG. 4(C) illustrates polymer thin film portion 141B1(t2) at a timeperiod (t2) subsequent to time ti, when patterned feature 143B1(t2) isdisposed in gap region 101B (i.e., where minimal gap distance Gseparates conveyors 110B and 120B). Due to the low viscosity and/or thinfilm thickness of the polymer thin film, the strength of electric fieldF(t2) causes patterned liquid polymer features 143B(t2) to separate fromadjacent polymer features (not shown) on first surface 111B. That is,because no additional surrounding fluid is available to supply thevertical growth of patterned feature 143B1(t2), web-like portion 141B11breaks away from adjacent features, whereby the liquid forming patternedfeature 143B1(t2) comprises a discreet “island” of liquid polymer.Specifically, the spacing and thickness of the polymer film arecontrolled such that the volume of liquid polymer drawn into eachpatterned feature (discreet liquid island) 143B1(t2) as it grows in thevertical (Z) direction (i.e., perpendicular to surface 111B) is equal tothe volume of fluid in the negative space of the pattern, the EHDpatterning process creates small particles of the same size scale as thepatterns.

FIG. 4(D) illustrates polymer thin film portion 141B1(t3) at a timeperiod (t3) immediately subsequent to time t2, when patterned feature143B1(t3) is disposed immediately downstream from the gap region (i.e.,where conveyors 110B and 120B are separated by a distance D21 that issubstantially equal to or slightly larger than the minimum gapdistance). At this point patterned feature 143B1(t3) a curing energy161B (e.g., UV laser light) “freezes” (solidifies) discreet feature143B1(t3) to form a solid micro-scale patterned particle (structure)145B. Note that this curing process is performed on every discreetfeature as it passes through the gap region, thereby generating multiplesolid micro-scale patterned particles disposed in a spaced-apartarrangement on conveyor surface 111B.

FIG. 4(E) illustrates micro-scale patterned particle 145B subsequent totime period t3. According to an embodiment of the present invention, aseparator device 170B (e.g., a knife edge) acts to separate micro-scalepatterned structure 145B from conveyor surface 111B.

FIG. 5 is a perspective view showing a system 100C according to apractical specific embodiment of the present invention in which thegeneralized conveyors mentioned above are implemented by parallel lowerand upper rollers (conveyors) 110C and 120C, the generalized thin filmformation device is implemented by a slot coater 140C, and thegeneralized curing device is implemented by a ultraviolet (UV) lightsource 160C, where these specific devices are controlled to perform aproduction method consistent with the generalized methods describedabove.

Referring to the lower portion of FIG. 5, lower roller 110C is operablycoupled to low voltage source 1500-1 such that it acts as the ground inthe electric field circuit. To generate the electric field, the outerperipheral portions of lower roller 110C are made up of either anelectrically conductive metal or an electrically conductive polymer, orouter surface 111C is optionally coated with an electrically conductiveand/or transparent material such as ITO.

Top roller 120C is operably coupled to high voltage source 150C-2 thatsupplies one or more high voltage signals to generate the appliedelectric field circuit. In one embodiment, outer surface 121C of toproller 120C includes a continuous conductive layer that is electricallyactive across the entirety of roller surface 121C. In other embodiments(discussed in additional detail below), top roller 120C includes eitheran electrode pattern or dielectric material to which a charge pattern isapplied.

Lower roller 1100 and upper roller 120C are driven by one or more motors1300-1 and 130C-2 using techniques known in the art such that eachregion of surface 111C through nip-type gap region 101C substantiallysimultaneously with a corresponding region of surface 121C (i.e.,rollers 110C and 120C are driven at matching speeds). Lower roller 110Cand upper roller 120C are maintained by a support structure (also notshown) such that they remain separated by a fixed minimum distance G ata nip (gap) region 101C. A conventional high precision nip system 180C,which is operably connected between the axis of rollers 110C and 120C tofacilitate adjustment of minimum distance G using known techniques,serves to guarantees high roller distance dimensional control.

Slot coater 140C coats (deposits) liquid polymer thin film 141C eitherdirectly onto cylinder roller surface 111C of lower roller 110C, or ontoa support web (not shown) that is disposed over surface 111C. Slotcoaters capable of performing this function are well known in the art.When polymer film 141C enters nip region 101C, it either replicates thepattern of electrodes disposed on upper roller 120C in the mannerdescribed below, or sets up a pattern based on the natural instabilityof the polymer system as described above.

To facilitate curing near the nip (gap) region 101C between rollers 110Cand 120C, UV curable polymers are utilized because of their fast fixingtime, and “fixing” mechanism is implemented by a system 160C (e.g., oneof an Ultra Violet (UV) curing system, an visible light curing system,and a focused thermal curing system) that directs beam 161C onto alocation adjacent to nip-type gap region 101C. Specifically, afterpassing through nip region 101C, beam 161C is applied such that thepolymer is cross-linked and hardens into the solid micro-scale patternshapes enforced on the liquid polymer by the applied electric field. UVlaser systems capable of performing this curing function are well knownin the art. In an alternative embodiment the curing system is disposedinside one of rollers 110C and 120C, and is directed through transparentroller material into gap region 101C. Solidified polymer film (notshown) is then removed from lower roller 110C and moved downstream forany additional steps that might be required.

The production output of system 100C is limited by two factors: thewidth W of rollers 110C and 120C, and the rotational speed Δθ of rollers110C and 120C. Roller width W is limited by the physical ability to bothmanufacture and install rollers 110C and 120C within the tolerancesrequired. These tolerances are similar to those in typical slot coatingsystems, which can reasonably be expected to maintain a 0.5 microntolerance over 3.5 meters. For one such realization of 8 micron featureswith a 2 micron tolerance, this leads to a maximum output of 1.3 m/swith fast UV cure times. The width can be increased and the sensitivityof the film pattern to machine tolerances can be adjusted for by varyingthe applied voltage through a number of electrode addressing schemesthat are explained in further detail below.

FIG. 6 is a simplified cross-sectional side view showing a system 100Daccording to another practical embodiment of the present invention.System 100D is characterized by a belt-to-belt arrangement formed by alower belt-like conveyor 1100 and an upper belt-like conveyor 120D thatare positioned to define an elongated gap region 101D between opposingplanar regions of lower belt surface 111D and upper belt surface 121D. Athin film deposition device (e.g., a slot coater) 140D is disposed toform a liquid polymer thin film 141D on lower belt surface 111D priorentering gap region 101D, and voltage sources (not shown) are connectedas described above to conductive material formed on the belts togenerate the desired electric field inside elongated gap region 101D.

The belt-to-belt arrangement of system 100D is similar to theroll-to-roll arrangement of 100C, but instead of a small nip-type gaparea of the roll-to-roll arrangement, system 100D provides a large gapregion that allows more time for the formation of the micro-scalepattern features. This arrangement facilitates the use of thermosettingpolymers by facilitating thermal curing (e.g., by way of thermal curingsystems (heater blocks) 160D disposed along the inside surface of thebelt material adjacent to elongated gap region 101D). To facilitatethermal curing, the belts are formed, for example, using a thermallyconductive material, or a transparent material for admitting IR lightinto elongated gap region 101D.

In order to maintain the tight tolerances required for the belt-to-beltprocess shown in FIG. 6, belt-like conveyors 110D and 120D must be heldclose by way of alignment blocks. This can either be achieved withsignificant amounts of tension or interlocking parts that slide in andout of the block using the arrangement indicated in FIG. 7.

FIG. 7 is a perspective cross-sectional view showing an interlockingarrangement according to a specific embodiment by which lower belt-likeconveyor 110D is maintained in a precise planar orientation relative toan upper surface of underlying heater block (or other support structure)160D. As indicated, lower belt-like conveyor 110D includes a carrierbelt portion 112D that slides over a planar upper surface 161D of heaterblock 160D such that patterned liquid features 143D form on conveyorsurface 111D according to one of the processes described above. Tomaintain precise Z-axis positioning relative to planar upper surface161D across the entire width of carrier belt portion 112D, heater block160D is constructed to define elongated T-shaped grooves 163D thatextend in the moving direction X of lower belt-like conveyor 110D, andlower belt-like conveyor 110D includes T-shaped ribs 113D that extendbelow upper belt portion 112D and are slidably received in correspondinggrooves 163D. Upper belt-like conveyor 120D (FIG. 6) is constructed witha similar arrangement, thereby providing a sliding tongue-and-groovetype arrangement that constrains the belts in the vertical direction andallows for tight tolerances to be achieved.

Belt-to-belt system 100D facilitates higher production output speeds(i.e., linear belt speeds). The belt tolerances are largely dictated bythe same tolerance limitations in the design of roll coating equipment.With precision machining it would be possible, in one possiblerealization to achieve a 0.5 micron tolerance over a 3.5 meter length.To create 8 micron features with a 2 micron tolerance over a 7 meter by7 meter area, the total linear speed of the belts in this realizationare limited to about 14 m/s. This realization is thus capable of muchhigher and industrially relevant throughput.

Due to the longer processing time provided by elongated gap region 101D,belt-to-belt system 100D facilitates operations that do not require acuring device (i.e., system 100D). In this case, polymer 141D is heatedand applied in a melted state onto surface 111D upstream of gap region101D. The polymer temperature is high enough to maintain the meltedstate as the polymer is patterned by the applied electric field in themanner described above. Once the pattern has been established, thepolymer is allowed to cool below the polymer's melting point temperatureto form solid micro-scale patterned structures 145D having one of theforms described above.

According to a preferred approach, in order to achieve the mostflexibility in creating and controlling the micro-scale patterns, thevarious systems described above (including both belt and rollerembodiments) are modified to include digital patterning control, whichis implemented using a dynamic charge generation mechanism thatfacilitates EHD patterning (i.e., electric field generation) byproducing a dynamic (variable) charge pattern on at least one of theconveyor surfaces, whereby the charge pattern defining the electricfield is dynamically alterable to compensate for system variances. Asset forth in the following exemplary embodiments, such dynamic chargegeneration is achieved using either segmented electrodes or a chargepatterning scheme.

FIG. 8(A) is a simplified diagram depicting a system 100E includes alower (first) conveyor 110E and an upper (second) conveyor 120E that areconstructed and arranged to convey a polymer thin film 141E through agap region 101E, where thin film 141E is generated on lower conveyorsurface 111E by a suitable device 150E and patterned by an electricfield F to form features 143E that are subsequently cured (e.g., by wayof UV light 161E) to form micro-scale structures 145E in a mannersimilar to that described above.

System 100E is characterized in that at least one of conveyors 110E and120E includes segmented electrodes that are digitally addressable by adynamic voltage source (electric field generator) such that eachindividual electrode receives an associated charge (voltage) having avalue determined, e.g., by experimental measurement performed prior toproduction operations. Specifically, upper conveyor 120E includessegmented upper electrodes 125E that are individually addressable bydynamic high voltage source (electric field generator) 150E-2 such thateach individual upper electrode (e.g., electrodes 125E-1 to 125E-5)receives an associated (e.g., unique/different or common/same) voltagevalue. Alternatively (or in addition), lower conveyor 110E includessegmented lower electrodes 115E that are digitally addressable bydynamic low voltage source (electric field generator) 150E-2 such thateach individual lower electrode (e.g., electrodes 115E-1 to 115E-5)receives an associated voltage value. Sources 150E-1 and 150E-2 areelectronic circuits produced in accordance with known techniques togenerate and deliver associated voltage values such that each segmentedelectrode (or each upper/lower electrode pair) produces an associatedportion of electric field F having an associated field strength. Forexample, upper electrode 125E-1 (or the pair formed by upper electrode125E-1 and lower electrode 115E-1) generate electric field portion F1 inthe region between conveyor 110E and 120E. Similarly, electrodes 125E-2to 125E-5 (or pairs 125E-2/115E-2, 125E-3/115E-3, 125E-4/115E-4 and125E-5/115E-5) generate electric field portions F2 to F5, respectively.

FIG. 9 is a perspective view showing a roller-type upper conveyor120E-1, which represents one type upper conveyor 120E used in system100E (i.e., conveyor 120E may also be implemented using a belt-typeconveyor). As indicated by conveyor 120E-1, segmented upper electrodes125E are arranged both along the rotational (circumferential) direction(i.e., as indicated in FIG. 8), and are also arranged along thecylindrical axis. That is, although the description related to FIG. 8refers to variable charge patterns occurring along the rotationaldirection of roller-type conveyor 120E-1, it is understood that variablecharge patterns discussed herein vary along the circumferential axisdirection as well. That is, all electrodes 125E of roller-type upperconveyor 120E-1 are independently addressable such that each electrodereceives an associated charge value.

Referring again to FIG. 8, segmented electrodes 125E allow digitalcontrol over the electric field generated in gap region 101E during EHDpatterning by facilitating the transmission of predetermined unique(different) or identical voltage values to each electrode, therebyallowing electrical correction (if needed) for physical variances thatinevitably arise in large systems requiring precise tolerances, such assystem 100E. That is, differences in localized electric field values F1to F5, which may be caused by electrode distance variations betweenneighboring electrodes 125E-1 to 125E-5 or between paired electrodes(e.g., electrodes 115E-1 and 125E-1) across gap region 101E, arecorrectable by transmitting a predetermined unique “high” voltage toeach electrode 125E-1 to 125E-5. For example, each electrode 125E-1 to125E-5 is individually addressed by dynamic high voltage source 150E-2and receives an associated voltage whose value is set such that eachelectric field portion F1 to F5 has uniform field strength. Note thatthe electrodes 125E arranged in the cylindrical axis direction (i.e., asshown in FIG. 9) are also individually addressed by dynamic high voltagesource 150E-2, and receive an associated voltage whose value is set suchthat each associated electric field portion also has a uniform fieldstrength. Exemplary segmented electrodes with individual addressingschemes suitable for implementing electrodes 115E and 125E are disclosedin co-owned U.S. Pat. No. 7,163,611, entitled CONCENTRATION AND FOCUSINGOF BIO-AGENTS AND MICRON-SIZED PARTICLES USING TRAVELING WAVE GRIDS,which is incorporated herein by reference in its entirety.

In alternative embodiments, at least some of segmented electrodes 125Ehave a modified (different) shape (e.g., line or point electrodes) thatcover different parts of the “counter” surface depending on the patternsneeded. Possible examples of line or point electrodes are disclosed inU.S. Pat. No. 7,163,611 (cited above). Other electrode shapes (e.g.,hexagonal or circular) are also possible, e.g., for making custom-shapedmicro-scale particles.

In alternative embodiments, the size and distances between electrodes isaltered to produce the desired EHD pattern. For example, although FIG. 8indicates that each electrode pair produces a single separatemicro-scale structure 145E, in other embodiments each electrode may besized to generate multiple features/structures. By controlling the shapeof the electrode a competing length scale to the intrinsic λmax isintroduced, which can either dominate the pattern formation dimension onthe 2D plane, or define the area for the intrinsic pillar pattern.

In other alternative embodiments, the voltages (charges) transmitted toeach segmented electrode is changed (i.e., increased or decreased) overtime, allowing for either custom pattern growth and or compensation offabrication variations across the patterning area. These voltages can beadjusted dynamically, to either achieve specific quality metrics in thefilm, or to adjust as processing conditions change leading to anextremely robust process.

FIG. 10 is a simplified diagram depicting another system 100F includinga lower (first) conveyor 110F and an upper (second) conveyor 120F thatare constructed and arranged to convey a polymer thin film 141F througha gap region 101F, where thin film 141F is deposited by device 140F andpatterned by an electric field F to form features 143F that aresubsequently cured to form micro-scale structures 145F in a mannersimilar to that described above. System 100F differs from the previousembodiment in that dynamic charge generation is achieved usingwell-defined charge patterns that are formed on an appropriateinsulating or semiconducting material layer 123F disposed on surface121F of upper conveyor 120F. In an exemplary embodiment first (e.g.,positive) charges are selectively applied in a predetermined pattern onlayer 123F by a first (e.g., positive) charge generating device 150F(e.g., a plasma generating device such as a scorotron) upstream of gapregion 101F, whereby the first charges generate corresponding portionsof electric field F in a manner similar to that described above withreference to the segmented electrode approach. In other embodiments,relatively high charges are applied to the electrodes on lower conveyor110F, and relatively low charges are applied to the electrodes of upperconveyor 120F. In some embodiments, the charge patterns are achieved byeither a masking process, or by a set of plasma generating devices ofthe required size. In other embodiments, a photo sensitive material,such as a photo receptor film similar to that used in a laser printer,is disposed on the upper conveyor, and the charge pattern is generatedby light transmitted onto the photo sensitive material, where laserbeam(s) are used to write a charge pattern on a photo receptor. Thecharge patterning approach provides an advantage in applications wheredifferent EHD patterns are needed in subsequent fabrication steps, or incontinuous patterning systems (i.e. where each sheet or section of thinfilm has a different pattern). The charge patterning approach gives thebiggest variability on the addressing electrodes, since the chargepattern can be changed easily from one step to the next, especially forthe case of optical charge generation (similar to Xerography).

Although the present invention has been described with respect tocertain specific embodiments, it will be clear to those skilled in theart that the inventive features of the present invention are applicableto other embodiments as well, all of which are intended to fall withinthe scope of the present invention. For example, although the variousexamples describe relatively high (e.g., positive) charges being appliedto the upper conveyor and relatively low (e.g., negative) being appliedto the lower conveyor, in other embodiments the associated electricfield is generated by reversing the applied charges (i.e., withrelatively high (e.g., positive) charges being applied to the lowerconveyor and relatively low (e.g., negative) being applied to the upperconveyor).

1. A method for continuously producing a plurality of micro-scalepatterned structures, the method comprising: disposing a liquid thinfilm on a first surface; moving the first surface such that the liquidthin film passes through a gap region defined between the first surfaceand an opposing second surface; generating an electric field in the gapregion such that the liquid thin film undergoes Electrohydrodynamic(EHD) patterning deformation during passage through the gap region,whereby portions of the liquid thin film form a plurality of patternedliquid features having a micro-scale patterned shape; and solidifyingthe plurality of patterned liquid features such that each of theplurality of patterned liquid features forms an associated solidmicro-scale patterned structure having said micro-scale patterned shape.2. The method of claim 1, wherein disposing the liquid thin filmcomprises depositing a liquid polymer on a conveyor using one of a slotcoating system, a slot die coating system, a slide coating system and acurtain coating system.
 3. The method of claim 1, wherein moving thefirst surface comprises moving the opposing second surfacesimultaneously with the first surface at a matching speed through thegap region such that a first surface region of the first surface passesthrough said gap region substantially simultaneously with acorresponding second surface region of said second surface.
 4. Themethod of claim 3, wherein the first surface and the second surface arerespectively disposed on first and second conveyors comprising one of anelectrically conductive material and a dielectric material; and whereingenerating the electric field comprises applying a first voltage to saidone of an electrically conductive material and a dielectric materialdisposed on the first conveyor, and applying a second voltage to saidone of an electrically conductive material and a dielectric materialdisposed on the second conveyor, the first voltage being different fromthe second voltage V2 such that said first and second voltages generatesaid electric field.
 5. The method of claim 1, wherein disposing theliquid thin film comprises depositing a UV curable liquid polymer on thefirst surface, and wherein solidifying the plurality of patterned liquidfeatures comprises directing a UV laser light onto the patterned liquidfeatures at a point adjacent to the gap region.
 6. The method of claim1, wherein disposing the liquid thin film comprises depositing athermosetting liquid polymer on the first surface, and whereinsolidifying the plurality of patterned liquid features comprisesdirecting heat energy onto the patterned liquid polymer featuresadjacent to the gap region.
 7. The method of claim 1, wherein disposingsaid liquid thin film comprises depositing a liquid polymer containingnanostructures such that said nanostructures are dispersed with initialorientations within said liquid polymer thin film, and whereingenerating said electric field comprises aligning the nanostructures ina substantially perpendicular orientation relative to the first surfacewithin the micro-scale patterned structure.
 8. The method of claim 1,wherein generating said electric field comprises causing said pluralityof patterned liquid features to separate from each other on said firstsurface, wherein said solidifying comprises solidifying said pluralityof separated patterned liquid features such that each said separatedpatterned liquid features forms a corresponding said solid micro-scalepatterned structure, and wherein said method further comprisesseparating said plurality of solid micro-scale patterned structures fromthe first surface.
 9. The method of claim 1, wherein moving the firstsurface and the opposing second surface comprises rotating first andsecond rollers arranged to define a nip-type gap region therebetween.10. The method of claim 9, wherein said solidifying comprises directingenergy from one of an Ultra Violet (UV) curing system, an visible lightcuring system, and a focused thermal curing system onto said patternedliquid feature at a location adjacent to said nip-type gap region. 11.The method of claim 1, wherein moving the first surface and the opposingsecond surface comprises directing first and second outer peripheralsurfaces of first and second belt-type conveyor structures along firstand second paths, respectively, where the first and second paths causesaid first and second outer peripheral surfaces to pass along anelongated gap region.
 12. The method of claim 11, wherein solidifyingthe patterned liquid polymer feature comprises directing heat energyfrom one of an Ultra Violet (UV) curing system, an visible light curingsystem, and a focused thermal curing system disposed inside one of saidfirst and second belt-type conveyor structures into said elongated gapregion.
 13. The method of claim 1, wherein generating an electric fieldcomprises generating a variable charge pattern on at least one of saidfirst surface and said second surface.
 14. The method of claim 13,wherein generating the variable charge pattern comprises individuallyaccessing each of a plurality of segmented electrodes disposed in anarray on said at least one of said first surface and said secondsurface, and transmitting an associated voltage to each of the pluralityof segmented electrodes.
 15. The method of claim 13, wherein generatingthe variable charge pattern comprises applying a first variable chargepattern on one of an insulating material layer and a semiconductingmaterial layer disposed on said at least one of said first surface andsaid second surface.
 16. A method for producing a plurality of separatemicro-scale patterned particles, the method comprising: disposing aliquid thin film on a first surface; moving the first surface such thatthe liquid thin film passes through a gap region defined between thefirst surface and an opposing second surface; generating an electricfield in the gap region such that the liquid thin film undergoesElectrohydrodynamic (EHD) patterning deformation during passage throughthe gap region, wherein said EHD patterning deformation causes saidliquid thin film to break up into a plurality of discreet liquidislands; and solidifying the plurality of discreet liquid islands suchthat each of the plurality of discreet liquid islands forms anassociated solid micro-scale patterned particle.
 17. The method of claim16, wherein disposing the liquid thin film comprises depositing a liquidpolymer on the first surface using one of a slot coating system, a slotdie coating system, a slide coating system and a curtain coating system.18. The method of claim 16, wherein solidifying the plurality ofdiscreet liquid islands comprises directing heat energy from one of anUltra Violet (UV) curing system, an visible light curing system, and afocused thermal curing system into said gap region.
 19. The method ofclaim 16, further comprising separating the plurality of solidmicro-scale patterned particles from the first surface.
 20. A method forcontinuously producing a plurality of micro-scale patterned structures,the method comprising: generating a variable charge pattern on at leastone of a first moving surface and a second second surface such that saidvariable charge pattern generates an electric field in a gap regiondefined between the first and second moving surfaces, said electricfield having sufficient strength to cause a liquid thin film disposed onthe first moving surface to undergo Electrohydrodynamic (EHD) patterningdeformation during passage through the gap region, whereby portions ofthe liquid thin film form a plurality of patterned liquid featureshaving a micro-scale patterned shape; and solidifying the plurality ofpatterned liquid features such that each of the plurality of patternedliquid features forms an associated solid micro-scale patternedstructure having said micro-scale patterned shape.